<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>
    <button>发送ajax请求</button>
    <script>
        let oBtn = document.querySelector('button');
        oBtn.onclick = function () {
            const xhr = new XMLHttpRequest();
            xhr.open('get', 'http://localhost:8080/type');
            // 设置响应数据类型
            xhr.responseType = 'json';
            xhr.send();
            xhr.onreadystatechange = function () {
                if (xhr.readyState === 4) {
                    if (/^2\d{2}$/.test(xhr.status)) {
                        console.log(xhr.response);
                    }
                }
            }
        }
    </script>
</body>

</html>